Memory-module controller, memory controller and corresponding memory arrangement and also method for error correction

ABSTRACT

A memory arrangement comprises a first memory module and a second memory module. An item of information to be written to the memory arrangement is written with a first address both to the first memory module and to the second memory module. When reading, the item of information is read either from the first memory module by means of the first address or from the second memory module by means of a second address differing from the first address. Subsequently a check is made as to whether the item of information is defective. If this is the case, the item of information is read from the respective other memory module.

RELATED APPLICATION—CLAIM OF PRIORITY

The present application claims the priority of German Patent ApplicationDE 10 2006 019 426.8 filed Apr. 26, 2006. This application claims thebenefit of the filing date of the referenced German Patent Applicationunder 35 U.S.C. §119. The present application is also a divisional ofU.S. application Ser. No. 11/740,762 filed Apr. 26, 2007. The content ofeach priority applications is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to a method for error correction for amemory arrangement and also to an appropriately configured memory-modulecontroller, to a memory controller and to a memory arrangement.

The present invention will be described in more detail in the followingwith reference to the single FIGURE on the basis of preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE represents a memory arrangement according to theinvention with four memory modules and with a memory controller forcontrolling the memory modules.

DESCRIPTION OF THE INVENTION

Memory modules—such as, for example, fully buffered DIMMs (Dual InlineMemory Modules)—do not have any built-in redundancy in order to correcterrors arising in their memory chips that exceed the error-correctingpossibilities of an ECC code (Error Checking and Correction code). Inthe course of the error correction by means of the ECC code, redundantbits are generated, starting from the bits to be stored pertaining to apredetermined item of information, which are stored together with thepredetermined bits. When reading, a check is now made by means of theECC code as to whether errors have occurred, whereby, depending on theseverity of the error and on the proportion of redundant bits withrespect to the bits stored overall, the error is either corrected ormerely recognized as such.

Although memory controllers are known that, with a view to avoidingerrors, mirror each bit to be stored or, to be more exact, store saidbit twice, such a method can be disadvantageous because the requisitebandwidth rises by 100%, because each bit is written twice by the memorycontroller.

According to an embodiment of the present invention, a method is madeavailable for error correction for a memory arrangement. In thisimplementation, the memory arrangement comprises a first and a secondmemory module which are both preferentially fully buffered dual in-linememory modules (DIMMs). An item of information to be stored in thememory arrangement is written to the first memory module under a firstaddress which is assigned to the first memory module. In the course ofwriting the item of information to the first memory module, the item ofinformation is simultaneously also written to the second memory modulewith the first address—i.e., the first address is both utilized in orderto write the item of information to the first memory module and utilizedin order to write the item of information to the second memory module.The item of information is accordingly stored simultaneously in thefirst and second memory modules by means of a write-instruction, and insuch an implementation, the second memory module may be regarded as aredundant memory module. For the purpose of reading the item ofinformation, the latter is read either from the first memory module bymeans of the first address, or from the second memory module by means ofa second address, differing from the first address, which can be derivedfrom the first address. Subsequently a check is made, for example bymeans of an ECC code, as to whether the item of information isdefective. If the item of information is defective—i.e., the item ofinformation also cannot be corrected by means of the ECC code—the itemof information is read from the respective other memory module, usebeing made of the first address when reading from the first memorymodule, and use being made of the second address when reading from thesecond memory module.

When writing data, because the item of information is writtensimultaneously—i.e., with the same write-instruction—both to the firstand to the second memory module, writing in this manner is advantageousbecause the bandwidth required for writing is not increased incomparison with a method that writes the item of information to onememory module only. When reading, because the item of information isonly read from both the first and the second memory modules when theitem of information is recognized as being defective upon first reading,the bandwidth required for reading is increased only in comparison witha method that reads the item of information from a memory module oncewhen the item of information is defective upon first reading, i.e., whenthe method that reads the item of information from a memory module onceonly has no possibility of reading or outputting the item of informationcorrectly. In other words, when reading the item of information in thesuccessful case—i.e., the item of information is not defective or can becorrected, for example by means of the ECC code—the bandwidth of themethod according to the invention is equal to the bandwidth of theconventional method which reads the item of information from a memorymodule once only.

According to another embodiment, the second memory module corresponds tothe first memory module with regard to its speed (clock frequency),memory capacity and memory organization (arrangement of ranks,addressing schema).

Generally, although the method according to the invention may alsooperate with a second memory module that does not correspond to thefirst memory module with regard to speed, memory capacity and memoryorganization, the method according to the invention becomessubstantially simpler if the first and second memory modules correspondwith regard to speed, memory capacity and memory organization or if thesecond memory module has a higher speed and a greater memory capacitythan the first memory module.

If the speed of the second memory module is lower than that of the firstmemory module, the method according to the invention would have to takethis lower speed of the second memory module into account when writingthe item of information. If the memory capacity of the second memorymodule lies below the memory capacity of the first memory module, themethod according to the invention would have to take this into account,to the effect that certain items of information are not written to thesecond memory module simultaneously, so that in the event of an errorthese items of information could not then be read from the second memorymodule.

In a preferred embodiment, in the course of reading the item ofinformation the item of information is read periodically from the firstand second memory modules alternately. In other words, when reading,before the corresponding item of information is checked for errors, afirst item of information is read from, for example, the first memorymodule, a second item of information is read from the second memorymodule, a third item of information is read from the first memorymodule, etc.

Because the item of information is checked for errors after being read,both with respect to the first memory module and with respect to thesecond memory module, whether an error is present is detected whenreading the item of information alternately from the first memory moduleand from the second memory module. If an error is present when the itemof information is read, this usually indicates that certain memory cellsof the memory module from which the item of information has been readare defective. Even if such an error can be corrected with the ECC code,it is an indication of the quality of the memory module, which can beused, for example, in order to inform an administrator about thedeclining quality of the corresponding memory module. If the item ofinformation is read from the first memory module only, and a readoperation from the second memory module is performed only if an error isdetected in the course of checking the item of information, the qualityof the second memory module would be unknown, which, in a worst case,could have the result that the second memory module has already failedas a result of being defective if a read operation is performedtherefrom because a defective item of information read from the firstmemory module.

Let it be pointed out that the method according to the invention is alsoapplicable to a memory arrangement that comprises several first and,correspondingly, several second memory modules. In this implementation,an item of information that is written to a particular first memorymodule is simultaneously also written to a particular second memorymodule assigned to the first memory module, so that, in accordance withthe invention, the item of information can be read either from theparticular first or from the particular second memory module, and in theevent of an error—i.e., if the item of information that has been read isuncorrectable—reading is effected from the respective other memorymodule.

Furthermore, in accordance with the invention it is possible thatseveral second memory modules have been assigned to one first memorymodule, so that an item of information that is written to the firstmemory module is written simultaneously to these several second memorymodules. In the course of reading the item of information, the latter isthen read from a memory module pertaining to a set that consists of thefirst memory module and the several second memory modules. Should it bedetected in the course of checking the item of information that thisitem of information is uncorrectable, the item of information is readfrom other memory modules pertaining to the set until the item ofinformation is present without errors. Hence, in accordance with theinvention, it is possible to reduce almost entirely the probability thatthe item of information will be misread in an uncorrectable manner byreason of memory errors.

Within the scope of the present invention a memory-module controller fora memory module, in particular for a fully buffered DIMM, is alsodisclosed. Upon receiving a write-instruction, the memory-modulecontroller according to the invention writes an item of informationassigned to the write-instruction to at least one memory chip of thememory module if a write-instruction address, which is an address usedfor write-instructions, has been assigned to the memory module. Uponreceiving a read-instruction, the memory-module controller reads theitem of information if a read-instruction address, which is an addressused for read-instructions, has been assigned to the memory module. Inthis implementation, the write-instruction address is not identical tothe read-instruction address, though it is known which write-instructionaddress corresponds with which read-instruction address.

By the write-instruction address not being identical to theread-instruction address, the memory-module controller can be configuredin such a manner that the memory-module controller stores each item ofinformation in the second memory module that is also stored by a firstmemory module. In this implementation, in the case of the first memorymodule the item of information is stored under the same address - moreprecisely the write-instruction address—under which address—moreprecisely the read-instruction address—the item of information is thenalso read. By the read-instruction addresses that have been assigned tothe second memory module being chosen in such a manner that they are notthe same as the read-instruction addresses that have been assigned tothe first memory module, an item of information can be read selectivelyeither from the first memory module or, by means of the memory-modulecontroller according to an implementation of the invention, from thesecond memory module.

According to an embodiment of the invention, the memory-modulecontroller is configured in such a manner that it, on one hand, passeson incoming data arriving at it—for example, read-instructions,write-instructions—to other memory modules, for example, and, on theother hand, temporarily stores said data in a buffer. Subsequently thememory-module controller evaluates the data in this buffer.

By the data being passed on immediately, it is ensured that the data canbe passed from one memory module to the next memory module almostwithout delay.

According to another embodiment of the invention, the memory-modulecontroller can also be configured in such a manner that thememory-module controller operates like a conventional commercialmemory-module controller. This means that the memory-module controlleraccording to the invention can be configured in such a manner that theitem of information is written to the memory module using the sameaddress—more precisely, the write-instruction address—under whichaddress—more precisely, the read-instruction address—the item ofinformation is then read from the memory module by means of thememory-module controller.

As a result, the memory-module controller according to implementationsof the invention, or a memory module that exhibits the memory-modulecontroller according to the invention, advantageously can be eitheremployed like a conventional commercial memory-module controller,respectively like a conventional commercial memory module, or, if thememory-module controller has been configured appropriately, employed insuch a manner that the memory-module controller according to theinvention, or the memory module, is employed for the purpose ofgenerating a type of security copy of the memory contents of an assignedmemory module.

Within the scope of the present invention a memory controller is alsomade available for a memory arrangement comprising several memorymodules. In this implementation, the memory controller writes an item ofinformation to be written to the memory arrangement under a firstaddress, which has been assigned to a first memory module, to this firstmemory module. In this implementation, the memory controller assumesthat the item of information is written simultaneously to a secondmemory module which has been assigned to the first memory module. Whenreading the item of information, the memory controller reads the item ofinformation either from the first memory module by means of the firstaddress or from the second memory module by means of a second address,which differs from the first address but which can be derived from thefirst address by the memory controller. Subsequently the memorycontroller checks whether the item of information that has been read isdefective or uncorrectable. If this is the case, the memory controllerreads the item of information from the respective other memory module,and in this implementation it uses the first address when reading fromthe first memory module, and uses the second address when reading fromthe second memory module.

Advantageously, when writing the item of information, the memorycontroller according to an implementation of the invention operates in amanner as a conventional commercial memory controller would operate, inwhich case of the item of information is written to one memory moduleonly. In other words, in comparison with conventional commercial memorycontrollers, the memory controller according to the invention exhibitsno disadvantage, for example, with respect to the band-width orprocessing-time required when writing the item of information, eventhough the item of information is written not just to one memory modulebut to two memory modules. Only when reading the item of informationdoes the memory controller according to the invention utilize implicitknowledge of the fact that the item of information has been written totwo memory modules, such that the memory controller reads the item ofinformation either from the first or from the second memory module.

Let it be pointed out that the memory controller according to theinvention could also be configured in such a manner that, prior to thecheck as to whether the item of information is defective, it alwaysreads the item of information from the first memory module, so that thebehavior of the memory controller according to the invention woulddiffer from the behavior of a conventional commercial memory controlleronly when the item of information that has been read is detected to bedefective. In this case, the memory controller according to theinvention would read the item of information from the second memorymodule, whereas a conventional commercial memory controller could onlyreport a read-error.

In another embodiment of the invention, the memory controller is capableof being configured via its basic input-output system (BIOS) in such amanner that it operates either as a conventional commercial memorycontroller or as previously described. If the memory controlleraccording to the invention has been configured via its BIOS in such amanner that it operates as a conventional commercial memory controller,prior to the error checking, it reads the item of information from thefirst memory module only and does not read the item of information fromthe second memory module, even when an error that is not correctable hasbeen detected upon reading the item of information from the first memorymodule.

Finally, within the scope of the present invention a memory arrangementis made available that comprises a first memory module and a secondmemory module, and also a memory controller for controlling the memorymodules. In this implementation, the memory arrangement passes an itemof information to be written to the first memory module and also to thesecond memory module in which the item of information is also stored.When reading the item of information, the memory arrangement reads theitem of information either from the first memory module by means of afirst address, with which the item of information has also been writtento the first memory module, or from the second memory module using asecond address which differs from the first address but which can bederived from the first address. If, in the course of a subsequent checkof the item of information which is carried out by the memoryarrangement, it turns out that the item of information exhibits an errorthat is not correctable, the memory arrangement reads the item ofinformation from the respective other memory module. In thisimplementation, when reading from the first memory module it uses thefirst address, and when reading from the second memory module it usesthe second address. Finally, the memory arrangement outputs the item ofinformation.

The advantages of the memory arrangement according to embodiments of theinvention correspond substantially with the advantages that previouslywere described in the discussion of the method according to theinvention, of the memory-module controller according to the invention,or of the memory controller according to the invention. Because theseadvantages were previously described, they will not be repeated here.

The present invention is preferable for use in memory arrangements thatemploy fully buffered DIMMs. However, the invention is, of course, notrestricted to this preferred field of application but may, for example,also be employed in memory arrangements in which a write-instructiondirected to a particular memory module reaches another memory module.

In the following description, exemplary embodiments of the presentinvention will be described in detail. It is to be understood that thefollowing description is given only for the purpose of illustrating theprinciples of the invention and is not to be taken in a limiting sense.Rather, the scope of the invention is defined only by the appendedclaims and is not intended to be limited by the exemplary embodimentsdescribed hereinafter.

The single FIGURE shows a memory arrangement 1 according to theinvention which comprises two first memory modules 3, 3′, two secondmemory modules 4, 4′ according to the invention and a memory controller2 according to the invention for controlling the four memory modules 3,3′, 4, 4′. In this implementation, the memory arrangement 1 exhibits twochannels 6, the first memory module 3 and the second memory module 4being assigned to the one channel, and the first memory module 3′ andthe second memory module 4′ being assigned to the other channel. The twochannels may be written to or read from simultaneously by the memorycontroller 2.

The memory controller 2 knows that the memory modules 3, 4, 3′, 4′ arearranged in groups 5, with the memory modules 3, 4 and the memorymodules 3′, 4′ each forming a group. In this implementation, both thefirst memory module 3, 3′ and the second memory module 4, 4′ of a groupstores the same item of information. In other words, the memory contentsof the two memory modules 3, 4, 3′, 4′ of a group 5 are identical.

Each memory module 3, 3′, 4, 4′ possesses memory chips 9 and an AMB(Advanced Memory Buffer) or, to be more exact, a memory-modulecontroller 10, 11. In this implementation, the memory-module controllers11 of the first memory modules 3, 3′ are each configured in such amanner that they operate like conventional commercial memory-modulecontrollers. Consequently the two first memory modules 3, 3′ operatelike conventional commercial memory modules—i.e., the memory controller2 reads an item of information from the first memory module 3, 3′ usingthe same address with which it has also written this item of informationto the corresponding first memory module 3, 3′. On the other hand, eachof the memory-module controllers 10 of the second memory modules 4, 4′is configured in such a manner that the second memory modules 4, 4′likewise store an item of information that is written by the memorycontroller 2 to the first memory module 3, 3′ assigned to the respectivesecond memory module 4, 4′.

The operation of an embodiment of the invention will be presented indetail in the following. Each memory module 3, 3′, 4, 4′ possesses amemory-module address, so that in a channel 6 the memory controller 2 isable to address either the first memory module 3, 3′ or the secondmemory module 4, 4′. This memory-module address is both an integral partof an address of a write-instruction and an integral part of an addressof a read-instruction. The memory-module controller 10 of the secondmemory module 4, 4′ is set up in such a manner that it interprets awrite-instruction which has actually been addressed with itsmemory-module address to the first memory module 3, 3′ as a storageinstruction addressed to its memory module 4, 4′ and stores the item ofinformation assigned to the write-instruction under the same address(i.e., the portion of the address of the write-instruction other thanthe portion identifying the memory-module address) in the second memorymodule 4, 4′ under which this item of information is also stored in thefirst memory module 3, 3′. The memory controller 2 is configured via itsBIOS in such a manner that it never uses the memory-module address ofthe second memory modules 4, 4′ in a write instruction.

The set-up of the memory-module controller 10 of the second memorymodules 4, 4′ in this implementation concerns only a central controlblock of the memory-module controller 10, with the set-up being effectedwith special bytes. Using these special bytes the memory-modulecontroller 10 is able to derive the memory-module address at which itstores the item of information if this memory-module address iscontained in the address of a write-instruction.

Since the two memory modules 3, 4, 3′, 4′ of a group 5 are connected tothe memory controller 2 using the daisy-chain principle, when awrite-instruction is received, the item of information is writtensimultaneously both to the first memory module 3, 3′ and to the secondmemory module 4, 4′. Because the item of information is writtensimultaneously both to the first memory module 3, 3′ and to the secondmemory module 4, 4′ with the same write-instruction, on the one hand thememory controller 2 is not further burdened by the additional storing ofthe item of information in the second memory module 4, 4′, and on theother hand the bandwidth required for writing the items of informationto the two memory modules 3, 4, 3′, 4′ is equal to a bandwidth withwhich the item of information is conventionally written to one memorymodule only.

In the course of a read-operation, the memory controller 2 is configuredvia its BIOS in such a manner that it reads an item of information to beread from the first memory module 3, 3′ and from the second memorymodule 4, 4′ alternately. In other words, the memory controller 2 knowsimplicitly that the item of information has been stored in the twomutually assigned memory modules 3, 4, 3′, 4′. Subsequently the memorycontroller 2 checks the item of information with the aid of the ECCcode. If in this implementation the memory controller 2 detects an errorthat is not correctable, the memory controller 2 reads the item ofinformation from the respective other memory module 4, 3, 4′, 3′.

If a temporal response of the memory arrangement 1 according to theinvention is compared with a temporal response of a conventional memoryarrangement, it is found that the temporal response when writing an itemof information is identical. This means that the memory arrangement 1according to the invention requires no additional time in comparisonwith a conventional memory arrangement in order to store the item ofinformation both in the first memory module 3, 3′ and in the secondmemory module 4, 4′. Also in the case of a successful first reading ofthe item of information—i.e., the item of information is error-free orcan be corrected by the ECC code—the temporal response of the memoryarrangement 1 according to the invention does not differ from thetemporal response of a conventional memory arrangement. Only if thememory controller 2 according to the invention detects, upon firstreading of the item of information, an error that is not correctable bythe ECC code does the temporal response of the memory arrangement 1according to the invention differ from the temporal response of theconventional memory arrangement, because the memory arrangement 1according to the invention reads the item of information a second timefrom the respective other memory module 4, 4′, 3, 3′. In thisimplementation, it is to be noted that in this case the conventionalmemory arrangement has no possibility of reading out the item ofinformation correctly. In other words, the memory arrangement 1according to the invention only requires more time than the conventionalmemory arrangement when it thereby also provides a genuine added valuein comparison with the conventional memory arrangement.

The memory arrangement 1 represented in the FIGURE could also be set upin such a manner that the second memory modules 4, 4′ behave likeconventional commercial memory modules. In this case the memorycontroller 2 is likewise configured like a conventional commercialmemory controller, so that an item of information to be stored is alsowritten explicitly to the second memory modules 4, 4′ by the memorycontroller 2, by the corresponding second memory module 4, 4′ beingaddressed by its memory-module address when a write-instruction isreceived.

In an embodiment of the invention which is not represented in theFIGURE, in each instance of each channel 6 of the memory arrangement 1additional groups of a first memory module and a second memory moduleassigned to this first memory module could be present. In thisimplementation, each first memory module of the further groups behavesin principle like standard commercial memory modules—i.e., the item ofinformation is written in the same memory-module address from it is alsoread, and each second memory module of the further groups behaves likethe initially described second memory modules 4, 4′—i.e., the item ofinformation is written with the memory-module address of the firstmemory module assigned to the respective second memory module and isread with the memory-module address of the respective second memorymodule.

Finally, instead of a single second memory module 4, 4′ several secondmemory modules could have been assigned to the first memory module 3,3′. In this case, a write-instruction of the memory controller 2, whichcontains as a memory-module address the memory-module address of thefirst memory module 3, 3′, would write the item of information both tothe first memory module 3, 3′ and to the second memory modules assignedto the first memory module 3, 3′. When reading the item of information,the memory controller 2 would read the item of information periodicallyfrom a memory module of a set that is composed of the first memorymodule and the second memory modules assigned to this first memorymodule. If the item of information that has been read is not correctableby the ECC code, the memory controller would read the item ofinformation from the other memory module pertaining to this set. If theitem of information is not correctable by means of the ECC code afterthis second reading, the memory controller would read the item ofinformation from yet another memory module pertaining to the set, thisbeing repeated until either an item of information that is correctableby the ECC code is present or until the memory controller has read theitem of information from all the memory modules pertaining to this set.

1. A memory-module controller for a memory module, wherein: thememory-module controller is configured, upon receiving awrite-instruction, to write an item of information corresponding to awrite-instruction to at least one memory chip of the memory module if anaddress corresponding to the write-instruction has been assigned to thememory module; the memory-module controller is configured, uponreceiving a read-instruction, to read out the item of information thathas been assigned to an address corresponding to the read-instructionfrom the at least one memory chip and outputs it via at least one outputterminal of the memory module if the address corresponding to theread-instruction has been assigned to the memory module; and the addresscorresponding to the write-instruction for the purpose of writing theitem of information is not identical to the address corresponding to theread-instruction for the purpose of reading the same item ofinformation.
 2. The memory-module controller according to claim 1,wherein the memory-module controller includes a memory-module controllerfor a fully buffered DIMM.
 3. The memory-module controller according toclaim 1, wherein the memory-module controller includes input terminalscorresponding to output terminals of the memory-module controller, andthe memory-module controller is configured such that one of: passes eachreceived instruction including one of the write-instruction orread-instruction applied to the input terminals of the memory-modulecontroller to the corresponding output terminals of the memory-modulecontroller; and temporarily stores in a buffer of the memory-modulecontroller, and wherein the memory-module controller subsequentlyevaluates the instruction stored in the buffer.
 4. The memory-modulecontroller according to claim 1, wherein the memory-module controller isconfigured to read the item of information with an address correspondingto the read-instruction, wherein the address corresponding to theread-instruction identical to the address corresponding with thewrite-instruction with which the item of information was written to thememory module by the memory-module controller.
 5. A memory arrangement,comprising: a first memory module; a second memory module; and a memorycontroller in communication with the first memory module and the secondmemory module and configured for controlling the first memory module andthe second memory module and for writing information to the first memorymodule and the second memory module, wherein the memory controller isfurther configured to: pass the item of information to be written to thefirst memory module to the second memory module; and write to the firstmemory module the item of information under a first address assigned tothe first memory module; and wherein the memory arrangement is furtherconfigured to: read the item of information from one of the first memorymodule and from the second memory module and check the item ofinformation for errors; when an error is detected, the memoryarrangement reads the item of information from a respective other memorymodule, wherein the second memory module is the respective other memorymodule of the first memory module and the respective other memory moduleof the first memory module is the second memory module; when readingfrom the first memory module, the memory arrangement uses the firstaddress and when reading from the second memory module, the memoryarrangement uses a second address differing from the first address; andoutput the item of information.
 6. The memory arrangement according toclaim 5, wherein: the first memory module and the second memory moduleare connected to the memory controller in the form of a chain using thedaisy-chain principle; and wherein the first memory module is the firstmemory module of this chain.
 7. The memory arrangement according toclaim 5, wherein the second memory module includes a memory-modulecontroller, wherein: the memory-module controller is configured, uponreceiving a write-instruction, to write an item of informationcorresponding to a write-instruction to at least one memory chip of thememory module if an address corresponding to the write-instruction hasbeen assigned to the memory module; the memory-module controller isconfigured, upon receiving a read-instruction, to read out the item ofinformation that has been assigned to an address corresponding to theread-instruction from the at least one memory chip and outputs it via atleast one output terminal of the memory module if the addresscorresponding to the read-instruction has been assigned to the memorymodule; and the address corresponding to the write-instruction for thepurpose of writing the item of information is not identical to theaddress corresponding to the read-instruction for the purpose of readingthe same item of information.
 8. The memory arrangement according toclaim 5, wherein the memory controller for the memory arrangement is amemory controller wherein: the memory controller is configured to writeto a first memory module an item of information to be written to thememory arrangement under a first address assigned to a first memorymodule of the several memory modules; the memory controller isconfigured to read the item of information either from the first memorymodule by means of the first address or from a second memory modulepertaining to the several memory modules by means of a second addressdiffering from the first address; the memory controller checks whetherthe item of information is defective; and when the memory controllerdetects that the item of information is defective, the memory controllerreads the item of information from a respective other memory module,wherein the second memory module is the respective other memory moduleof the first memory module and the respective other memory module of thefirst memory module is the second memory module and the memorycontroller using the first address in the case of reading from the firstmemory module and using the second address in the case of reading fromthe second memory module.
 9. The memory arrangement according to claim5, wherein the memory arrangement is configured for writing an item ofinformation to the memory arrangement to the first memory module under afirst address assigned to the first memory module; writing the item ofinformation to the second memory module using the first address; readingthe item of information from one of the first memory module by means ofthe first address and from the second memory module by means of a secondaddress differing from the first address; and checking whether the itemof information is defective; and when the item of information isdefective, the item of information is read from a respective othermemory module such that the second memory module is the respective othermemory module of the first memory module and the respective other memorymodule of the first memory module is the second memory module, the firstaddress being used in the case of reading from the first memory module,and the second address being used in the case of reading from the secondmemory module.